1. Field of the Invention
This invention relates to static wheel balancers for determining the balance of vehicle wheels, and more particularly, it relates to static wheel balancers of the type having a pivot ball for supporting a wheel balancing head upon a vertical support post.
2. Description of the Prior Art
The principle of a common type of static wheel balancer is in itself a simple one. The wheel (with a mounted tire) is placed on a wheel balancing head mounting a bubble level for indicating unbalance. The head is supported by a hard steel ball or sphere which rests on the anvil of a post or other vertical support means that is normally coaxial with the wheel and balancing head. If the wheel to be balanced is out of balance, the wheel balancing head will tilt out of a horizontal plane, and this tilt will manifest itself by an off-center reading of the bubble level. The balance error is usually corrected by the application of one or more balance weights to the rim flange of the wheel. Balancers of this type subject the pivot ball and supporting structure to shock loads if a heavy wheel and tire assembly is initially dropped onto the balancing head while the pivot ball is supported by the anvil, and special means are often provided to protect the ball from these heavy shock loads.
The U.S. Pat. No. 3,055,221, issued Sept. 25, 1922 to Bageman et al. discloses a static wheel balancer of the afore-described type having a vertical support post formed with a flat faced tappet or anvil. The balancing head is pivotally supported on the anvil by a pivot ball rigidly mounted in the balancing head. A cam mechanism is provided to lower the anvil so that the balance head rests on a support sleeve projecting from the base of the balancer when the wheel is first placed on the balance head. The anvil must be mechanically lifted to support and free the balance head for wheel balancing.
A similar pivot ball and anvil construction for supporting the balancing head is shown in U.S. Pat. No. 3,164,996 issued Jan. 12, 1965 to Carrigan and assigned to the FMC Corporation. This patent also shows structure for lowering the anvil during initial wheel application, and the anvil must be mechanically lifted for the balancing operation. Furthermore, in this patent, the wheel centering cone of the balancing head is resiliently supported to minimize damage to the pivot ball and the supporting anvil from impacts that occur when a wheel assembly is dropped onto the balancing head. The latter feature is incorporated in the preferred embodiment of the present invention.
The U.S. Pat. No. 3,280,640, issued Oct. 25, 1960 to Fuertges, also employs a single pivot ball rigidly mounted on the balance head and supported on an anvil. In this patent, the anvil post is slidably mounted in a post support and guide sleeve. The post is initially lifted from its wheel balancing position by a spring. When the wheel is placed on the balancing head, the post is lowered against the force of the spring until the lower end of the post is solidly seated on a shoulder at a lower portion of the sleeve. Oil bleed holes in the sleeve, valved by the descending post, are provided to control deceleration of the post until it bottoms out on the sleeve shoulder for the balancing operation.